Method and apparatus for testing sealed envelopes



E. LEMMERS Feb. 27, 1945.

'METHOD AND APPARATUS FOR TESTING SEALED ENVELOPE S Filed Jan. 21, 1942 m, w mm m e 0 T M Vv. v 1A Im S w; H 9 b Patented Feb. 21, 1945 METHOD AND APPARATUS FOR TESTING SEALED ENVELOPES Eugene Lemmers, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application'January 21, 1942, Serial No. 427,597

8 Claims.

My invention relates to method and apparatus for the production of a high frequency glow discharge within a sealed container. More particularly, my invention relates to method and apparatus for testing photoflash lamps of thewellknown type used for photographic purposes for the presence of air within the sealed bulb thereof by the production of a high frequency glow discharge therein.

As a safeguard against explosion of the glass bulb when flash lamps of the above type are flashed, it is common practice, in the manufacture of such. flash lamps, to test the completed lamp for the presence of air. One'well-known method of conducting such a test, known as a coil or glow test, consists in the use of high frequency equipment for the production of a high frequency glow discharge within the sealed lamp bulb. By observing the-color of the glow discharge produced in the lamp bulb, the presence or absence of air therein can then be readily de termined, a pale bluish-green glow discharge denoting a good lamp containing the normal oxygen gas filling with no air present and a purplish or pink-colored discharge indicating a lamp into which air has leaked.

Heretofore, in such high frequency glow testing of flash lamps, it has been customary to connect one side of the high frequency circuit to the lamp leading-in wires through the lamp base, and the other side to an external electrode placed closely adjacent the top of the lamp bulb. However, such an arrangement is apt to produce a spark or discharge within the lamp bulb at the primer head or fulminating substance therein.

' or at a point closely adjacent thereto, which will result in the ignition of the primer head or fulminating material with consequent flashing of the lamp. This is particularly true in the case of flash lamps of the fulminating bead type disclosed and claimed in copending application Serial No. 328,399, Marvin Pipkin, filed April 8, 1940. now Patent 2,291,983, issued August 4, 1942, in which the light-producing material consists solely of one or more beads or coatings of a readily ignitable fulminating material disposed on the tips of the inner lamp leads. To overcome thi defect, therefore, it has been found necessary to provide suitable means, preferably in the form of an electrical conductor or antenna connected to one of theinner lamp leads and extending to a point within the bulb considerably removed from the fulminating material, for confining the glow discharge to an area within the bulb considerably removed from the fulminating material so as to prevent the discharge from striking the fulminating material and accidentally igniting the same with resultant premature flashing of the lamp. Such a flash lamp construction i shown and claimed in the copending applications of D. E. Elmendorf, Serial Nos. 371,318 and 384,622, filed December 23, 1940, and March 22, 1941, respectively, the latter of which is now Patent 2,342,575, issued February 22, 1944. While such a flash lamp construction is entirely satisfactory insofar as the prevention of flashouts' during the high frequency testin of the lamp is concerned, nevertheless the use of the conductor or antenna member complicates the manufacture of the flash lamp and increases its 9 cost somewhat.

Qne object of my invention is to provi e a method and apparatus for producing a high frequency discharge in a given portion of the space within a sealed envelope.

Another object of my invention is to provide a method and apparatus for producing, in a sealed envelope, a high frequency discharge between two relatively closely spaced points on the wall of the envelope by the application of the high frequency electrodes to the'external surface of the envelope wall.

Still another object of my invention is to provide a method and apparatus for testing flash lamps for the presence of air therein by the production of a high frequency discharge in the sealed lamp bulb which will not set off and prematurely flash the lamp.

A further object of my inventionis to provide a method and apparatus for producing a high frequency discharge within the sealed bulb of a flash lamp between two spaced points'on the bulb surface such that the discharge path within the bulb is remote from the fulminating material disposed therein.

An important feature of the invention is the provision of two spaced electrodes which are connected to the opposite terminals of a source of high frequency current and which are adapted to be placed in contact with or closely adjacent the sealed flash lamp bulb at two spaced points on the curved surface thereof so that the discharge gap therebetween is remote from the fulminating material in the lamp bulb, together with a liquid insulating medium disposed between the said electrodes and contacting that portion of the bulb wall between the said spaced points thereon engaged by the electrodes so as to compel the high frequency discharge between the electrodes to pass through the interior of the lamp bulb rather than along the exterior surface thereof.

Further objects and advantages of my invent on will appear from the following description of a species thereof and from the accompanying drawing which is a diagrammatic illustration of an arrangement according to the invention for testing flash lamps for the presence of air therein.

' Referring to the drawing, the apparatus, ac-

of the high frequency discharge electrodes of.

the device. For making electrical connection from the exterior of the cup III to the mercury filling l3 therein, a leading-in wire I4 is sealed through the bottom wall of the glass cup I so as to extend into and terminate within-th mercury filling.

Filling the receptacle Ill up to a level high enough to just cover the mercury l3, for instance, about to /8" or so, is a suitable liquid insulating medium I 5. A supernatant [6, in the form of a suitably electrically conductive liquid,

covers the liquid insulating medium 15 to a depth of about or so. The supernatant electrically conductive liquid [6 serves as the otherhighfrequency discharge electrode of the device. The two liquids l5 and I6 should be immiscible in one another and, in addition, the electrically conductive supernatant l6 should be/of appreciably lower specific gravity than that of the liquid insulating medium l5, so that t e two liquids l5, I8 will maintain their separate/ state at all times with the liquid insulating m ium l5 always at the bottom of the receptacle Ill. The electrically conductive supernatant [6 may conveniently consist of water. In such case, the liquid insulating medium preferably consists of either trichlorethylene or carbon tetrachloride. However, any other suitable liquid mediums possessing the requirements mentioned above may be employed.

Disposed concentrically within the receptacle l0 and resting against the bottom wall thereof is an inverted dish-shaped support member I! of insulating material, such as glass, having a centrally located opening l8 therein through which projects the bulb IQ of the flash lamp to be tested. The said opening 18 is located below the point of maximum diameter of the lamp bulb l9 and is of such a diameter that the periphery thereof just engages the wall of the bulb when the tip portion 2| of the latter is seated in proper position in the seat II at the bottom of the receptacle H). The peripheral wall of the opening I8 thus serves to support the bulb l9 in an upright position within the receptacle III. p

When the lamp is in proper testing position within the receptacle so that the tip portion 2! of the bulb l9 contacts the mercury l3 in the seat I I, the liquid insulating medium [5 and the supernatant liquid electrode l6 will also contact the surface of the bulb at different points thereof. The insulating medium l5, however, because of its greater specific gravity than that of the supernatant liquid I6, will always separate the supernatant liquid I6 from the mercury l3 and will always contact a definite length or portion 22 of the bulb surface between the portion 2| in contact with the mercury l3 and the portion 23 in contact with the supernatant liquid l6.

To produce the high frequency discharge within the lamp bulb, the mercury electrode l3 and the supernatant electrode I6 are connected to a suitable source of high frequenc current of high potential. Thus, the supernatant [8 may be grounded, as shown, and the mercury l3 connected, by leading-in wire II, to one end of the secondary 25 of a Tesla coil 24, the other end of which is grounded. The primary 26 of the Tesla coil is then connected to a suitable source 21 of high frequency current, as shown.

When the high frequency source 21 is energized, and th lamp 20 is inserted in proper testing position within the receptacle ill, a high frequency glow discharge is formed within the lamp bulb 19 between the two electrodes [3 and l6; and because of the application of the high frequency to portions 2|, 23' of the bulb remote from the fulminating material 28 of the flash lamp, the glow discharge is. formed at a point within the bulb likewise remote from the fulminating material 28. Consequently, there is no possibility of the glow discharge accidentally igniting the fulminating material 28 and so prematurely flashing the lamp. By visually observing the color of the high frequency glow discharge produced within the lamp bulb, th presence or absence of air therein can then be readily determined.

The use of an insulator l5 of liquid form, which intimately contacts the outer surface of the bulb wall, enables the formation within the bulb of a glow discharge of relatively small size between two relatively closely spaced points on the bulb wall. Without such a liquid insulator IS, the discharge would form exteriorly of the bulb, since the breakdown potential of the air gap between the relatively closely spaced external electrodes would be less than the breakdown potential of the space within the bulb which is adjacent to such electrodes. The above indicated possibility of forming a very small discharge between two relatively closely spaced points on the bulb wall is of particular utility in the case of flash lamps of the above mentioned fulminating bead type employing a bulb of relatively small size, since with such small sized flash lamps the glow discharge within the bulb must be confined to a relatively small area therein remote from the fulminating material in the bulb if ignition of such fulminating material by the glow discharge, and therefore premature flashing of the lamp, is to be avoided.

The presence of the liquid insulating medium I5 between the supernatant liquid electrode l6 and the mercury l3 in an amount sufficient to prevent a breakdown thereof, and the intimate contact of the liquid insulating medium IS with the intervening surface 22 of the 'bulb wall, prevents the passage of the high frequency discharge between the electrodes l3 and I6 along the outside surface of the bulb wall. In this manner, the

formation of the high frequency discharge within the lamp bulb, rather than exteriorly thereof, is

positively assured.

In place of determining the presence or absence of air within the lamp bulb by visual examination of the color of the high frequency glow discharge produced therein, such determination can be made instead by means of a reading on a suitable form of meter. Thus, one or more photoelectric cells 29 having a substantial sensitivity to the so-called near ultraviolet radiations, i. e., radiations having a wave length of from about 3400 to 3600' Angstrom units, may be disposed within the receptacle In so as to be directed'or pointed at that portion of the flash lamp bulb l9 within which the high frequency glow discharge is formed during the testing of the lamp. In addition, a suitable cover or shield 30 is arranged to cover the receptacle l0, when the lamp 2!! is in proper test position therein, to act as a light trap serving to prevent any light exteriorly of the receptacle from entering the latter and exciting the photoelectric cells 29 therein. Preferably, the cover or shield 30 is in the form of two metal plates having recesses 3| therein for the accommodation of the base 32 of the lamp to be tested, the plates being pivotally mounted to rotate about a vertical axis so as to permit insertion of the lamp in, and removal from the receptacle l0.

By connecting the photoelectric cells to a suitable galvanometer or other current measuring device (not shown), the readings recorded by such meter will then readily and accurately indicate the absence or the presence of air within the lamp bulb. Thus, a good flash lamp having no air present in the bulb but only the normal oxygen gas filling therein, will yield substantially noreading on the galvanometer since a discharge in oxygen gives substantially no radiations in the ultraviolet region, to which radiation the photoelectric cells 29 are predominantly sensitive. On the other hand, any lamp having air (and therefore nitrogen) present in the bulb, will give at least an easily readable deflection of the galvanometer needle since a mere trace of nitrogen in the bulb will cause the glow discharge to emit a substantial amount of radiations in the 3400 to 3600 Angstrom unit band to which radiation the photoelectric cells 29 are particularly sensitive.

Where the flash lamp to be tested is of the fulminating bead type shown in the drawing, and described and claimed in the above mentioned Pipkin Patent 2,291,983, then the lamp is preferably provided with a small internal electrode or conductive member disposed within the top portion of the bulb on the inner surface of the bulb or extending alongside thereof, as disclosed and claimed in my copending application Serial No. 427,598 filed of even date herewith, now Patent 2,316,344, issued April 13, 1943. Such an internal electrode or conductor member serves to shorten the discharge gap through the space within the lamp bulb between the external mercury electrode 13 and the external liquid electrode l6, and therefore facilitates the starting of the glow discharge within the lamp bulb.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for producing a high frequen y discharge in a sealed envelope of insulating material comprising a receptacle having a quantity of mercury disposed therein at the bottom thereof, a liquid insulating medium in said receptacle covering the said mercury, a supernatant on said liquid insulating medium consisting of an electrically conductive liquid immiscible with and of lower specific gravity than said liquid insulating medium, and a source of high frequency current connected to the said mercury and the said electrically conductive supernatant.

2. Apparatus for producing a high frequency discharge in a sealed envelope of insulating material comprising a receptacle having a quantity of mercury disposed therein at the bottom thereof, a liquid insulating medium in said receptacle covering the said mercury therein, said liquid insulating medium being immiscible with and of higher specific gravity than water, a supernatant on said liquid insulating material consisting of water, and a source of high frequency current connected to the said mercury and the said water supernatant.

3. Apparatus for determining the presence of air in a sealed envelope, said apparatus comprising a substantially light-tight container in which the sealed envelope to be tested is positioned, means for producing a high frequency glow discharge within said envelope, a photoelectric cell arranged to be exposed to the radiation of the said glow discharge in said envelope, said photoelectric cell having a substantial sensitivity to radiations in the near ultraviolet region which are produced when atmospheric nitrogen is present in the envelope, and indicating means for indicating the degree of excitation of said photoelectric cell.

4. The method of producing a high frequency discharge in a sealed envelop of insulating material which comprises immersing a portion of the envelope in a liquid medium comprising two separate and distinct electrically conductive liquids, separating said liquids by a relatively thin layer of a liquid insulating medium so that the outer surface of the said portion of the en- 'velope is in contact with both of said electrically conductive liquids and connecting said electrically conductive liquids to a source of high frequency current to thereby produce a high frequency glow discharge within the said portion of the envelope.

5. Apparatus for testing the atmosphere in sealed bulbs of insulating material by a high frequency discharge comprising a pair of electrodes adapted to engage and terminate at the exterior bulb surface at spaced points thereon, a source of high frequency current connected to said electrodes, and an insulating medium so disposed in the space between said electrodes as to intimately contact the exterior surface of the bulb and inhibit passage of the discharge through any path outside the bulb.

6. Apparatus for testing the atmosphere in sealed bulbs of insulating material by a high frequency discharge comprising a receptacle containing a pair of spaced electrodes separated by a liquid insulating medium, one of said electrodes being below the surface of said insulatin medium, the said electrodes being so spaced and arranged that upon insertion of a portion of a bulb therebetween they engage the exterior surface of the bulb at spaced points thereon and the liquid insulating medium contacts the exterior bulb surface between the electrodes to inhibit passage of the discharge through any path outside the bulb, and a source of high frequency current connected to said electrodes.

7. Apparatus for testing the atmosphere in sealed bulbs of insulating material by a high frequency discharge comprising a receptacle having an electrode at the bottom thereof, a liquid insulating medium in said receptacle covering the said electrode, a supernatant on said liquid insulating medium consisting of an electrically conductive liquid immiscible with and of lower specific gravity than said liquid insulating medium, and a source of high frequency current connected to the said electrode and the said supernatant.

8. The method of producing a localized high frequency discharge in a sealed glass envelope which comprises connecting a source of high frequency to a pair of electrodes, placing said pair of electrodes against closely spaced points on the external surface of said envelope and inhibiting passage of the discharge through any path outside the envelope by maintaining an insulatin medium in intimate contact with the portion of the envelope between said electrodes.

EUGENE LEMMIERS. 

